Thermal properties of esterified cassava starches and their maltodextrins in various water systems

Abstract

Esterified cassava starches were prepared by reaction with three types of acid anhydride (1–4% dsw of acetic anhydride, succinic anhydride, and octenyl succinic anhydride), yielding acetylated (AC), succinylated (SC), and octenyl succinylated (OSA) starches with different degrees of substitution (DS = 0.006–0.039). Their thermal properties, i.e. the glass transition temperature (Tg) at limited water content (13%) and retrogradation at intermediate (50%) and excess (70%) water content were evaluated by a differential scanning calorimeter (DSC) in order to elucidate the effect of substituted groups. At limited water system, the substitution of ester groups on starch molecules caused changes in Tg; the changes were dependent on substituent characteristics and contents. With respect to increasing free volume induced by the substitution of hydroxyl groups with large ester group of octenyl succinyl, OSA starches had lower Tg, while this effect was not observed for AC and SC starch, presumably because of their low MWs. In both intermediate and excess water systems, esterification at low DS did not cause dramatic change in onset gelatinization temperatures. Starch retrogradation in excess water system was the lowest for OSA starch. The Avrami equation exhibits the highest half‐time (t1/2) of recrystallization and the lowest rate constant (k) of retrogradation for OSA. The Tg of most esterified cassava maltodextrins (DS ≈ 0.02, 0.03; Dextrose Equivalent, DE<2 and 3<DE<6) had decreased significantly (p<0.05) with increasing DE except OSA maltodextrin with DS 0.024 was not significantly different (p>0.05).